The latest data from NASA and the University of Colorado at Boulder's
National Snow and Ice Data Center show the continuation of a decade-long
trend of shrinking sea ice extent in the Arctic, including new evidence for
thinning ice as well.

The researchers, who have been tracking Arctic sea ice cover with satellites
since 1979, found that the winter of 2008-09 was the fifth lowest maximum
ice extent on record. The six lowest maximum events in the satellite record
have all occurred in the past six years, according to CU-Boulder researcher
Walt Meier of NSIDC.

The new measurements by CU-Boulder's NSIDC show the maximum sea ice extent
for 2008-09 reached on Feb. 28 was 5.85 million square miles, which is
278,000 square miles below the average extent for 1979 to 2000, an area
slightly larger than the state of Texas, said Meier.

In addition, a team of CU-Boulder researchers led by Research Associate
Charles Fowler of the Colorado Center for Astrodynamics Research, or CCAR,
has found that younger, thinner ice has replaced older, thicker ice as the
dominant type over the past five years, making it more prone to summer melt.

"Ice extent is an important measure of the health of the Arctic, but it only
gives us a two dimensional view of the ice cover," said Meier. "Thickness is
important, especially in the winter, because it is the best overall
indicator of the health of the ice cover. As the ice cover in the Arctic
grows thinner, it becomes more vulnerable to summer melt."

Until recent years, measurements have shown most Arctic ice has survived at
least one summer and often several, said Meier. But the balance has now
flipped, and seasonal ice -- which melts and re-freezes every year -- now
comprises about 70 percent of Arctic sea ice in winter, up from 40 to 50
percent in the 1980s and 1990s, he said. Thicker ice that has survived two
or more years now comprises just 10 percent of ice cover, down from 30 to 40
percent in years past.

Scientists believe Arctic sea ice functions like an air conditioner for the
global climate system by naturally cooling air and water masses, playing a
key role in ocean circulation and reflecting solar radiation back into
space.

In a related study led by Ron Kwok of NASA's Jet Propulsion Laboratory in
Pasadena, Calif., researchers have demonstrated a way to estimate ice
thickness over the entire Arctic Ocean. Using two years of data from NASA's
Ice, Cloud and Land Elevation Satellite, or ICESat, the team made the first
basin-wide estimate of the thickness and volume of the Arctic Ocean ice
cover for 2005 and 2006.

"With the new data on the area and thickness of Arctic sea ice, we can now
better understand the sensitivity and vulnerability of the ice cover to
changes in climate," Kwok said.

A recent study by a team from CU-Boulder's CCAR concluded there has been a
near complete loss of the oldest, thickest Arctic ice, and that 58 percent
of perennial ice was only two to three years old. In the mid-1980s, only 35
percent of that sea ice was that young and that thin, according to aerospace
engineering sciences department Research Professor James Maslanik, who led
the 2008 study published in *Geophysical Research Letters*.

"Heading into the 2009 summer melt season, the potential continues for
extensive ice retreat due to the trend toward younger, thinner ice that has
accelerated in recent years," said Maslanik, also a member of the
Cooperative Institute for Research in Environmental Sciences. "A key
question will be whether this second year ice is thick enough to survive
summer melt," said Maslanik.

"If it does, this might start a trend toward recovery of the perennial sea
ice pack," Maslanik said. "If it doesn't, then this would be further
evidence of the difficulty of re-establishing the ice conditions that were
typical of 20 or 30 years ago."

The Arctic ice cap grows each winter as the sun sets for several months and
intense cold sets in. The total volume of winter Arctic ice is equal to the
volume of fresh water in Lake Superior and Lake Michigan combined.

While some sea ice is naturally pushed out of the Arctic by winds, much of
it melts in place. First-year sea ice usually reaches 6 feet in thickness,
while ice that has lasted through more than one summer averages 9 feet and
can grow much thicker in some locations near the coast.
###

A massive ice shelf anchored to the Antarctic coast by a narrow and quickly
> deteriorating ice bridge could break away soon, the European Space Agency
> warned Friday.
>
> The Paris-based agency said satellite images show the bridge that connects
> the Wilkins Ice Shelf to Charcot and Latady Islands "looks set to collapse."
>
> "The beginning of what appears to be the demise of the ice bridge began
> this week when new rifts" appeared and a large block of ice broke away, it
> said.
>

This is the tenth major ice shelf to collapse in recent times. If you are
going to worry about something ice shelves are a bigger deal than sea ice.
Think of sea ice as ice cubes in your drink. If they melt they don't make
your drink take up any more volume. The relevance of sea ice is as a canary
in the mine. Ice shelves do increase your sea surface level and are
susceptible to unpredictable effects such as the ice bridge collapse on the
Wilkins. Because of this IPCC AR4 punted on predicting this effect and gave
the false impression that sea level rise is less than it will be.

Rich Blinne
Member ASA

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Received on Mon Apr 6 13:53:30 2009